This invention relates generally to electrooptic displays of the electrochromic type, wherein a persistent electrochromic material undergoes reversible and stable color changes upon the application of an electric field. More particularly, the invention relates to a thin electrochromic display suitable for manufacture in a continuous process.
Electrochromic displays are well known in the art, examples being shown in U.S. Pat. No. 4,012,831 issued Mar. 22, 1977 to Leibowitz and assigned to the present assignee, which describes a process for making an electroreactive layer on the rear electrode used in an electrochromic display by surface oxidizing and subsequently heat treating in hydrogen a tungsten metal layer on a ceramic base. When the ceramic base is used as a substrate, this substantially adds to the thickness of the display.
Electrochromic displays built up in layers from the front substrate are known in the art using solid or crystalline electrolytes as ion carriers to enable alternately darkening or bleaching the electrochromic material when a field is applied across the electrolyte. Examples of such displays may be seen in U.S. Pat. No. 4,009,936 issued to Kasai or Mar. 1, 1977, U.S. Pat. No. 3,995,943 issued to Jasinski or Dec. 7, 1976 and U.S. Pat. No. 3,971,624 issued to Bruesch et at on July 27, 1976. The Jasinski and Kasai patents utilize a sealant layer of thermosetting plastic or epoxy resin to enclose a layer of metallic silver and the solid electrolyte, and require extension of the silver layer or an external electrode passing through the sealant to make electrical contact. The Bruesch et al patent utilizes a thin exposed metal layer applied on top of an electrochromic material.
The foregoing Jasinski, Kasai, and Bruesch et al patents, while having possibilities for reducing the thickness of electrochromic displays from the older more bulky displays using two substrate members, nevertheless are built up in layers from the single transparent substrate and do not readily lend themselves to mass production or to continuous processing. Also the layer thickness and processes require great care to achieve uniform results.
Accordingly, one object of the present invention is to provide an improved thin electrochromic display which is adapted for continuous process manufacture.
Another object of the invention is to provide an improved construction for a thin electrochromic display of uniform and consistent quality.